Aftermarket AFM system.
Depending on the type driver he is this product could be great or a pain in the tail.
But before jumping out and buying one a few figures should be crunched.
The advertisement is for "as much as 22% fuel savings"
What would 22% savings amount to on the vehicle?
How much does that equate to in $$?
How long will this product have to be used to pay itself off?
In the end it may not be worth the time, expense, and effort.
Not to be a jerk here but a Tahoe is not ever gonna get good mileage, if you want good mileage sell the Tahoe and buy something smaller with less cylinders to feed, some things are just a fact and cant be changed.
He might be able to improve his mileage on the Tahoe with a few cheaper methods.
Check tire pressures, check tire sizes.
Next oil change go to synthetics for engine and trans.
Drive with more care, i.e. easy on the starts, coast to stops etc., hyper mileage tecniques.

It appears to be the same thing as the AFM on my 5.3 that is a total waste of money, in my opinion. It never seems to work when it should be and mileage on my 2010 is lower than my 86 suburban that was a 4bbl carb.
To me it all seems to be smoke and mirrors until someone can actually prove day to day results. Theory is great but I here more complaints about the 5.3 with AFM